Systems and methods for providing alignment in total knee arthroplasty

ABSTRACT

Systems and methods for providing alignment in total knee arthroplasty operations are provided herein. The systems and methods generally include a plurality of sensors coupled to a patient&#39;s bones or other surgical tools, the sensors detect their position and orientation in space and communicate this information to a processor. The processor can utilize the information to display data to a surgeon or other user regarding the position, angle, and alignment of a patient&#39;s bones, surgical tools, and the reconstructed knee joint.

FIELD OF THE INVENTION

The present invention relates to surgical procedures and, in particular,to systems and methods for aligning anatomical structures and surgicalcomponents during total knee arthroplasty operations.

BACKGROUND

Total Knee Arthroplasty

The knee is the largest joint in the human body. As shown in FIGS. 1 and7A, the knee 100 includes the lower end of the femur 102 (thigh bone),the upper end of the tibia 104 (shin bone), and the inner surface of thepatella 106 (knee cap, see FIG. 7A). The femur rotates over the tibiaand the patella glides in a groove on the end of the femur in front(i.e., anterior). The inner surface of these bony components is coveredby cartilage 106 that, along with joint fluid, provides smooth motion ofthe joint and shock absorption. Various ligaments and muscles help inkeeping the knee strong and stable.

Arthritis is a condition where the cartilage 106 starts wearing away andthe knee becomes stiff and painful. FIGS. 2 and 3A illustrate a kneeexhibiting osteoarthritis, including deterioration of the cartilage 106.As the condition worsens, bone can rub against bone, causing even morepain and loss of function. Knee replacement surgery, also known as kneearthroplasty, is the indicated treatment for many arthritic jointconditions and involves replacing the painful joint with an artificialprosthesis. During knee replacement surgery, the proximal end of thetibia and the distal end of the femur are exposed by an incision made infront (i.e., anterior) of the knee. These bony structures are then cutand shaped to accept prosthetic implants, as shown in FIG. 3B. FIG. 4illustrates alternative views of knee arthroplasty prosthesis, includinga polyethylene implant 402 that is often placed on an inner surface ofthe patella during the procedure.

FIG. 5 illustrates one embodiment of a total knee prosthesis 500 inisolation. The prosthesis 500 typically includes four components:

-   -   1. Femoral component 502, made of a metal material and designed        to replace the articular surface and subchondral bone of the        distal end of the femur 102;    -   2. Tibial component 504, made of a metal material and designed        to replace the subchondral bone of the proximal tibia 104. This        component can also be formed from alternative materials, such as        polyethylene;    -   3. Insert 506, typically formed from polyethylene and designed        to provide a bearing surface between the femoral and tibial        components 502, 504. It is typically fixed over the tibial        component 504 by a locking mechanism; and    -   4. Patella component 402, made from polyethylene as described        above and designed to replace the articular surface of the        patella.        Total Knee Arthroplasty (TKA), when successful, can result in        rapid improvement in pain, joint function, and quality of life        for a majority of patients.

The frequent success of the procedure, in combination with an agingpopulation, has caused demand for TKA procedures to increase rapidly. In2003 alone, 402,100 TKA operations were performed. With a continuedrapid increase in demand, there are projected be close to 3.5 millionTKA operations in 2030. The increasing demand for this procedure willput a burden on the health care system in at least two ways: (1) bystressing the number of well trained surgeons and (2) by increasingoverall expense.

One strategy to help meet this demand is to reduce the requiredoperation time and improve the outcome of TKA procedures. Spending lesstime during a primary TKA, and eliminating the need for any subsequentrevision procedure, will save time and allow for a higher volume ofthese procedures to be performed.

Recurrent Surgical Problems

Arthritic knee joints usually present with different degrees ofdeformity and misalignment because of various degradations and changesin cartilaginous and bony components of the joint. Compared to thenormal knee anatomy 602 shown in FIG. 6, there are typically twodifferent types of misalignment: (1) varus deformity 604 (i.e., bowlegged) and (2) valgus deformity 606 (i.e., knock knees). One importantgoal of a TKA procedure is to restore optimal biomechanical alignment ina reconstructed joint. This is because a properly aligned joint willhave better function, result in higher patient satisfaction, andincrease the longevity of the reconstructed joint.

Proper alignment can be achieved by making different cuts in the distalfemur and proximal tibia in relation with various planes and axes ofthese long bones. As shown in FIGS. 7A-7C and 8 illustrate a typicalprogression of a TKA operation, in which various cuts are made in thefemur and tibia to prepare the bones to receive prostheses. To make thecuts, any of a variety of cutting guides (also known as cutting blocksor jigs) are typically placed next to the bones after they are exposed.The cutting guides provide a reference plane for cutting the bone usinga special saw. As can be expected, the cutting blocks have to beprecisely positioned at proper angles relative to the bone to ensurecorrect placement of the prostheses and subsequent alignment of thereconstructed joint. Accordingly, any of a variety of alignment devicescan be employed to position the cutting guides, including, for example,the femoral intramedullary alignment device 900 shown in FIG. 9 and thetibial extra-medullary alignment device 1000 shown in FIG. 10.

Unfortunately, most alignment devices available today and designed forthis purpose are either not precise enough, very expensive, or both.Indeed, the bone cuts, and consequently the reconstructed jointalignment, is often not as it was intended to be when using thesedevices.

Currently Available Options

There are three classes of alignment devices currently available:

-   -   1. Mechanical instruments, including intramedullary or        extra-medullary devices like those shown in FIGS. 9 and 10;    -   2. Computerized navigation systems, which utilize specialized        computers, stereoscopic cameras, and marker structures to track        the three-dimensional positioning of objects attached to the        marker structures; and    -   3. Custom-made cutting blocks that align with the shape of a        specific patient's bones in a manner that results in correctly        oriented bone cuts.

More recently, another option has been introduced that involves creatinga custom set of prostheses for each particular patient's anatomy. All ofthese options, however, suffer from the problems mentioned above—thatis, they are extremely expensive, too imprecise, or both. In addition,the patient-specific devices and prostheses can require additional timeand visitation with a surgeon to image the patient's anatomy, design thecustom components, and fabricate them in advance of a TKA procedure.

SUMMARY

The systems and methods described herein address the problems discussedabove by providing more accurate and more precise alignment ofanatomical structures, prostheses, and surgical tools during total kneearthroplasty (TKA) operations. In general, the systems and methodsdescribed herein employ a plurality of sensor units capable of detectingtheir position and orientation in space and communicating thatinformation to a digital data processor. By attaching the sensors to anyof a patient's bone, a calibration instrument, a cutting guide, or othersurgical tools, software executing on the digital data processor candetermine the three-dimensional position of, for example, the patient'sbones (e.g., the femur and tibia), the cutting guides, or othertools/instruments. The positions of one or more of these components canbe updated continuously throughout the operation, and can aid surgeonsin more efficiently and more accurately completing a TKA procedure. Thesystems and methods described herein have a number of advantages overthe prior art, including increased accuracy and precision, as well asreduced cost due to simple configuration and the use ofreadily-available components. In addition, the systems and methodsdescribed herein can be easily reused with multiple patients withoutrequiring the fabrication of custom components.

In one aspect, a system for optimizing the alignment of a bone cuttingguide for placement of a total knee prosthesis component is providedthat includes a first bone sensor that can be adapted to be fixed to afirst bone and has a sensor for determining the orientation of the firstbone sensor and a transmitter for transmitting orientation datawirelessly. The system can further include a first bone guide having aplurality of probes configured to contact anatomical features of thefirst bone to establish a known geometry with respect to a mechanicalaxis of the first bone. The first bone guide can include a first boneguide sensor having a sensor determining the orientation of the firstbone guide and a transmitter for transmitting orientation datawirelessly. The system can also include a first bone cutting guidehaving one or more features for attaching to the patient's anatomyproximate to the first bone. The first bone cutting guide can include afirst bone cutting guide sensor having a sensor determining theorientation of the first bone cutting guide and a transmitter fortransmitting orientation data wirelessly. The system can further includea processing unit comprising a computer processor coupled to anon-transitory memory and a display. The memory can store softwareinstructions causing the computer processor to: (i) receive orientationdata wirelessly from the first bone sensor, (ii) receive orientationdata wirelessly from the first bone guide sensor, (iii) apply theorientation data from the first bone guide sensor and the first bonesensor to calculate angular offsets that calibrate the first bonesensor's orientation data to reflect the orientation of the mechanicalaxis of the first bone, (iv) receive orientation data wirelessly fromthe first bone cutting guide sensor, and (v) display to a user adifference between the orientation of the mechanical axis of the firstbone and the orientation of the first bone cutting guide.

The systems and methods described herein can include any of a variety ofadditional or alternative features and/or components, all of which areconsidered within the scope of the present invention. For example, thesystems and methods described herein can be applied to a number ofdifferent anatomical structures in the body. In some embodiments, forexample, the first bone can be a tibia. In such embodiments, the firstbone guide can include at least one tubercle probe and at least onemalleolus probe. In other embodiments, the first bone guide can furtherinclude a spine probe and at least two malleolus probes. In still otherembodiments, the first bone cutting guide can be arranged to guide a cutthat is oriented at a 90 degree angle to the mechanical axis of thefirst bone, though, in other embodiments, different orientation anglescan be utilized.

In certain embodiments, the first bone can be a femur rather than atibia. In such embodiments, the first bone guide can be configured tocontact the femoral shaft. In addition, the first bone guide can includetwo parallel and equal height probes for contacting the femoral shaft.

In some embodiments, the system can further include a second bone sensorthat can be adapted to be fixed to a second bone and can have a sensorfor determining the orientation of the second bone sensor and atransmitter for transmitting orientation data wirelessly. The system canalso include a second bone guide having a plurality of probes configuredto contact anatomical features of the second bone to establish a knowngeometry with respect to a mechanical axis of the second bone. Thesecond bone guide can include a second bone guide sensor having a sensordetermining the orientation of the second bone guide and a transmitterfor transmitting orientation data wirelessly. The system can furtherinclude a second bone cutting guide having one or more features forattaching to the patient's anatomy proximate to the second bone, and thesecond bone cutting guide can include a second bone cutting guide sensorhaving a sensor determining the orientation of the second bone cuttingguide and a transmitter for transmitting orientation data wirelessly.Furthermore, the non-transitory memory of the processing unit canfurther include software instructions causing the computer processor to:(i) receive orientation data wirelessly from the second bone sensor,(ii) receive orientation data wirelessly from the second bone guidesensor, (iii) apply the orientation data from the second bone guidesensor and the second bone sensor to calculate angular offsets thatcalibrate the second bone sensor's orientation data to reflect theorientation of the mechanical axis of the second bone, (iv) receiveorientation data wirelessly from the second bone cutting guide sensor,and (v) display to a user a difference between the orientation of themechanical axis of the second bone and the orientation of the secondbone cutting guide.

As noted above, in certain embodiments the first bone can be a tibia andthe second bone can be a femur. In this manner, the positions andorientations of both bones can be tracked throughout the course of anoperation to provide feedback to surgeons implanting a prostheticdevice.

In another aspect, a computer implemented method for aligning a cuttingguide for a total knee arthroplasty in a patient using a processing unitcomprising a computer processor coupled to a non-transitory memory, areceiver, and a display is provided. The method can include receiving bythe processing unit orientation data wirelessly from a first bone sensorattached to the patient's first bone, and receiving by the processingunit orientation data wirelessly from a first bone guide sensor, wherethe first bone guide sensor is attached to a first bone guide thatincludes probes for interfacing with the first bone in a known geometry.The method can further include calculating by the processing unit, basedon the orientation data from the first bone guide sensor and the firstbone sensor, angular offsets that calibrate the first bone sensor'sorientation data to reflect the orientation of the mechanical axis ofthe first bone. The method can also include receiving by the processingunit orientation data wirelessly from a first bone cutting guide sensorthat is attached to a first bone cutting guide that is connected to thepatient, and displaying by the processing unit to a user a differencebetween the orientation of the mechanical axis of the first bone and theorientation of the first bone cutting guide.

As with the system described above, the computer implemented method caninclude any of a variety of additional or alternative steps or features.For example, in some embodiments the first bone can be a tibia, while inother embodiments the first bone can be a femur. In still otherembodiments, the first bone cutting guide can be arranged to guide a cutthat is oriented at a 90 degree angle to the mechanical axis of thefirst bone, though other angular orientations can also be employed.

In certain embodiments, the method can further include receiving by theprocessing unit orientation data wirelessly from a second bone sensorattached to the patient's second bone, and receiving by the processingunit orientation data wirelessly from a second bone guide sensor, wherethe second bone guide sensor is attached to a second bone guide thatincludes probes for interfacing with the second bone in a knowngeometry. The method can also include calculating by the processingunit, based on the orientation data from the second bone guide sensorand the second bone sensor, angular offsets that calibrate the secondbone sensor's orientation data to reflect the orientation of themechanical axis of the second bone. Still further, the method caninclude receiving by the processing unit orientation data wirelesslyfrom a second bone cutting guide sensor that is attached to a secondbone cutting guide that is connected to the patient, and displaying bythe processing unit to a user a difference between the orientation ofthe mechanical axis of the second bone and the orientation of the secondbone cutting guide.

In such embodiments, the first bone can be a tibia and the second bonecan be a femur. Accordingly, the method can provide a surgeon withvaluable feedback regarding the orientations of each bone.

In still another aspect, a method for aligning a cutting guide for totalknee arthroplasty on a patient is provided that includes attaching afirst bone sensor to the patient's first bone, where the first bonesensor can include a sensor for determining the orientation of the firstbone sensor and a transmitter for transmitting orientation datawirelessly. The method can also include contacting a first bone guide tothe patient's first bone, where the first bone guide has a plurality ofprobes configured to contact anatomical features of the first bone toestablish a known geometry with respect to a mechanical axis of thefirst bone, and where the first bone guide includes a first bone guidesensor having a sensor determining the orientation of the first bone.The method can further include comparing the orientation data from thefirst bone guide sensor to the orientation data from the first bonesensor to calibrate the first bone sensor with respect to a mechanicalaxis of the first bone. The method can also include applying a firstbone cutting guide to the patient's first bone, where the first bonecutting guide has one or more features for attaching to the patient'sanatomy proximate to the first bone, and where the first bone cuttingguide includes a first bone cutting guide sensor having a sensordetermining the orientation of the first bone cutting. The method canfurther include comparing the orientation data from the first bonesensor with the orientation data from the first bone cutting guidesensor to determine the alignment between the first bone cutting guideand the mechanical axis of the patient's first bone.

As with the embodiments described above, the first bone can be a tibiain certain embodiments, and can be a femur in other embodiments.Further, in certain embodiments the cutting guide can be arranged toguide a cut that is oriented at a 90 degree angle to the mechanical axisof the first bone.

In some embodiments, the method can further include attaching a secondbone sensor to the patient's second bone, where the second bone sensorhas a sensor for determining the orientation of the second bone sensorand a transmitter for transmitting orientation data wirelessly. Themethod can also include contacting a second bone guide to the patient'ssecond bone, where the second bone guide has a plurality of probesconfigured to contact anatomical features of the second bone toestablish a known geometry with respect to a mechanical axis of thesecond bone, and where the second bone guide includes a second boneguide sensor having a sensor determining the orientation of the secondbone guide. The method can further include comparing the orientationdata from the second bone guide sensor to the orientation data from thesecond bone sensor to calibrate the second bone sensor with respect to amechanical axis of the second bone. The method can also include applyinga second bone cutting guide to the patient's second bone, where thesecond bone cutting guide has one or more features for attaching to thepatient's anatomy proximate to the second bone, and where the secondbone cutting guide includes a second bone cutting guide sensor having asensor determining the orientation of the second bone cutting guide.Still further, the method can include comparing the orientation datafrom the second bone sensor with the orientation data from the secondbone cutting guide sensor to determine the alignment between the secondbone cutting guide and the mechanical axis of the patient's second bone.

In such embodiments, the first bone can be a tibia and the second bonecan be a femur. Accordingly, the method can provide a surgeon withvaluable feedback regarding the orientations of each bone. In addition,any of the various features or embodiments described above can becombined in any of a variety of manners, even if not stated explicitlyhere.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the normal anatomy of a right knee;

FIG. 2 illustrates an osteoarthritic right knee;

FIG. 3A illustrates another osteoarthritic right knee

FIG. 3B illustrates a total knee arthroplasty;

FIG. 4 illustrates prosthetic components implanted during kneearthroplasty;

FIG. 5 illustrates an alternative view of prosthetic componentsimplanted during knee arthroplasty

FIG. 6 illustrates (from left to right) normal, varus, and valgus kneealignments;

FIG. 7A illustrates one embodiment of pre-operative anatomy of a rightknee;

FIG. 7B illustrates bone cuts to the knee of FIG. 7A required duringknee arthroplasty;

FIG. 7C illustrates one embodiment of post-operative anatomy of the kneeof FIG. 7A;

FIG. 8 illustrates one embodiment of a simplified procedure for kneearthroplasty;

FIG. 9 illustrates one embodiment of an intra-medullary alignment deviceused for cutting the distal femur;

FIG. 10 illustrates one embodiment of an extra-medullary alignmentdevice used for cutting the proximal tibia;

FIG. 11 illustrates components utilized in one embodiment of a systemaccording to the teachings of the present invention;

FIG. 12 illustrates one embodiment of a femur guide;

FIG. 13 illustrates one embodiment of a tibia guide;

FIG. 14 illustrates one embodiment of a pin guide;

FIG. 15 illustrates anatomic and mechanical axes of a femur asdetermined in the templating step described below;

FIG. 16 illustrates an anatomic axis of the tibia (which is the same asa mechanical axis of the tibia) as determined in the templating stepdescribed below;

FIG. 17 illustrates step 1(a) of the templating portion of a procedureaccording to the teachings of the present invention;

FIG. 18 illustrates step 1(b) of the templating portion of a procedureaccording to the teachings of the present invention;

FIG. 19 illustrates step 1(c) of the templating portion of a procedureaccording to the teachings of the present invention;

FIG. 20 illustrates step 1(d) of the templating portion of a procedureaccording to the teachings of the present invention;

FIG. 21 illustrates step 1(e) of the templating portion of a procedureaccording to the teachings of the present invention;

FIG. 22 illustrates step 1(f) of the templating portion of a procedureaccording to the teachings of the present invention; and

FIG. 23 illustrates one embodiment of a display window of applicationsoftware according to the teachings of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention includes a novel apparatus, as well as a uniquemethodology and system, to measure, calculate, and monitor alignment ofthe long bones of the human lower limb for precise intra-operative bonepreparation and positioning of prostheses, particularly with respect toavoiding misalignment of the reconstructed knee joint.

The systems described herein generally include a plurality of measuringsensor units that can detect their position and orientation inthree-dimensional space and communicate this information to a digitaldata processor, e.g., via a wireless communication protocol. Themeasuring sensor units described herein can utilize inexpensive, highlyaccurate, digital components that are able to communicate with softwarerunning on a computer processor, personal computer (PC), or hand-heldelectronic device (e.g., a smartphone or electronic tablet), toaccurately determine three-dimensional positioning of the femur and thetibia, as well as the angular position of cutting blocks or instruments.The positioning of these components can be monitored throughout thepreparation of the bones to ensure that the reconstructed knee joint isproperly aligned once the procedure is completed.

The determination of these positions and angles can be seen and read bya surgeon via a visual display, such as a portable digital display,thereby removing the need for a PC in certain embodiments. In someembodiments, the measuring system can continuously monitor the positionof a patient's lower limbs and, as a consequence, the surgeon caneffectively ensure an accurate angular placement of the cuttinginstruments in order to prepare the patient's native bone and restorethe appropriate alignment of the leg. This can result in optimumfunctionality of the reconstructed joint and increase the patient'ssatisfaction following surgery.

The position sensing and monitoring systems described herein can be fastand easy to use, as well as accurate and precise in its determinations.Furthermore, it can be cost-efficient to operate. For example, thesystems described herein require neither sophisticated equipment norelaborate machinery, and are able to directly display the cutting guideinstrument's placement, thereby avoiding any misalignment andeliminating the need for subsequent revision procedures to achievestability in the reconstructed knee joint. In short, the devices,systems, and methods described herein can provide a precise and reliabletool for proper placement of prosthetic components during kneearthroplasty.

Words, Terms, and Titles

Although many of the words, terms, and titles employed herein arecommonly employed and conventionally understood in their traditionalmedical usage and surgical context, a summary of detailed descriptiveinformation and definitions is presented below for some human anatomicsites, for specific medical phrases and surgical applications, and forparticular jargon, designations, epithets, or appellations. These pointsof information, descriptions, and definitions are provided herein toavoid the misinformation, misunderstandings, and ambiguities which oftenexist; as an aid and guide to recognizing the particulars of the presentinvention; and for appreciating the true scope and breadth of thepresent invention.

Anatomical Axis of the Femur: a straight imaginary line passing throughthe middle and along the shaft of the femur. An example anatomical axisof the femur 1502 is shown in FIG. 15.

Mechanical Axis of the Femur: a straight imaginary line that connectsthe center of rotation of the hip joint to the center of the knee. Anexample mechanical axis of the femur 1504 is shown in FIG. 15.

Anatomical Axis of the Tibia: an imaginary line passing through themiddle and along the shaft of the tibia. An example anatomical axis ofthe tibia 1602 is shown in FIG. 16.

Mechanical Axis of the Tibia: the same line as the anatomical axis ofthe tibia.

Alignment: the relation between the mechanical axis of the femur and thetibia.

Varus Deformity: when the intersection of the mechanical axis of thetibia and that of the femur falls outside the knee joint, resulting in abowlegged deformity. An example of a varus deformity 604 is shown inFIG. 6.

Valgus Deformity: when the intersection of the mechanical axis of thetibia and that of the femur falls inside the knee joint, resulting in aknock-kneed appearance. An example of a valgus deformity 606 is shown inFIG. 6.

Slope: the angle between the cut surface of the tibia or the tibialcomponent and the axis of the tibia in the coronal plane.

Anteroposterior (AP) View: an x-ray view taken from the front of thebody to the back.

Lateral View: an x-ray taken from one side of the body.

System of the Invention/Components

The invention is primarily adapted for use in knee arthroplastyoperations. It includes a novel system and a unique methodology tomeasure, calculate, and monitor position angles and alignment ofelements of a patient's leg for precise intra-operative placement offemoral and tibial prostheses, particularly with respect to avoidingmisalignment of the reconstructed joint.

FIG. 11 illustrates the basic components of one embodiment of a systemaccording to the teachings of the present invention. The system 1100 caninclude one or more sensors 1102 that include a sensor capable ofdetecting the three-dimensional position and orientation of the sensor1102 in space, as well as a transceiver or other communication componentcapable of transmitting position and/or orientation information toanother component in the system. As explained in more detail below, thesensors 1102 can be coupled to various bones in the patient's body, aswell as a variety of surgical guides, cutting blocks, or otherinstruments. The system 1100 can also include a digital data processor1104 coupled to a non-transitory digital data store 1106, a display1108, and a wireless transceiver 1110 or other communications component.The non-transitory digital data store 1106 can be any kind ofcomputer-readable media, with the exception of a transitory, propagatingsignal. As explained below, the processor can receive information fromthe sensors 1102 via the transceiver 1110, and can execute applicationsoftware stored in the data store 1106 to calculate any of a variety ofinformation regarding the position of the patient's bones and alignmentof the reconstructed joint. Results can be displayed to a surgeon orother user via the display 1108, which can be any of a variety ofdigital displays or other user interfaces known in the art.

More specifically, one embodiment of a system according to the teachingsof the present invention can include one or more of the followingenumerated elements:

-   -   1. A digital templating software, for evaluating the axes of        long bones of the lower limb, i.e., the femur and the tibia, and        measuring alignment and angles of flexion and/or extension of        the knee joint.    -   2. An electronic tibia position sensor (TS), capable of sensing        its orientation in 3-dimensional space and transmitting the        information to the computer processor 1104. The TS can be        attached to the shaft of the tibia and can transmit the position        angles of the tibia to the computer processor 1104 and        application software (see items 6 and 7 below). The position        sensors 1102 used herein (including the TS and others described        below) can each have at least one orientation sensor and at        least one transmitter. The transmitter can be any of a variety        of types used to transmit information, e.g., wirelessly, to a        computer or tablet. In one embodiment, the sensors can include a        BLUETOOTH transceiver. The orientation sensors can specify the        tilt of the sensor with respect to orthogonal axes (such as        x-y-z axes) and heading with respect to an external field (e.g.,        a natural or man-made magnetic field, etc.). In exemplary        embodiments, accelerometers can be used to determine tilt and a        magnetometer can be used to specify orientation with respect to        natural or man-made magnetic fields.    -   3. An electronic femur position sensor (FS), capable of sensing        its orientation in 3-dimensional space and transmitting the        information to the computer processor. The FS can be attached to        the shaft of the femur and can transmit the position angles of        the femur to the computer processor 1104 and application        software (see items 6 and 7 below). The FS sensor can be        constructed similarly to the TS described above, and one        embodiment of an exemplary FS 1700 is shown in FIG. 17.    -   4. A tibia axis guide (TG), an instrument used to reproduce the        anatomic axis of the tibia. An exemplary tibia axis guide 1300        is shown in FIG. 13. The TG 1300 can include a metal frame with        an attached electronic position sensor 1302 capable of sensing        its orientation in 3-dimensional space and transmitting the        information to the computer processor and application software        (see items 6 and 7 below). The TG 1300 can in some embodiment        include a vertical element 1304 on which the sensor 1302 is        positioned. A superior (i.e., upper) end of the vertical element        1304 can include a spine probe 1306 and a tibial tubercle probe        1308. An inferior (i.e., lower) end of the vertical element can        include two malleolus probes 1310, 1312. As will be explained        below, the various probes on the TG 1300 can be used to locate        the relevant anatomical features on the spine to establish the        mechanical axis of the patient's tibia.    -   5. A femur axis guide (FG), for reproducing the anatomic axis of        the femur. An exemplary femur axis guide 1200 is shown in        FIG. 12. The FG 1200 can include an embedded electronic position        sensor capable of sensing its orientation in 3-dimensional space        and transmitting the information to the computer processor and        application software (see items 6 and 7 below). The FG 1200 can        also include a sensor 1202 (extending vertically in FIG. 12)        with two probes 1204, 1206. The two probes 1204, 1206 (extending        horizontally in FIG. 12) can be parallel and have the same        length. As explained below, the probes 1204, 1206 can be used to        contact the shaft of the femur to establish its orientation in        at least one plane.    -   6. A computer processor (e.g., processor 1104), capable of        running the application software (see item 7 below) and        receiving the transmitted data from the various position sensors        (e.g., the TS, FS, TG and FG). The computer processor can be a        server, desktop, laptop, tablet, smart phone or any other        stationary or mobile computer device having a processor coupled        to a transceiver (e.g., transceiver 1110) that can communicate        with the sensors described above, a memory (e.g., data store        1106) that can store sensor data and contain software        instructions that will cause the processor to execute the        functions disclosed herein, and a display (e.g., display 1108)        for providing results to a user.    -   7. Application software, capable of (i) receiving the        information transmitted by the TS, FS, TG and FG; (ii)        calculating the various angles and/or positions of differing        surgical tools and patient anatomy as described below, and (iii)        displaying the position angles and calculating the angular        relationships that aid a surgeon in placing the various guides        and cutting blocks used in total knee arthroplasty. The        application software can run on the computer processor described        above.    -   8. A pin guide for placing pins on the patient's anatomy to        which one of the above-described sensors can be attached. An        exemplary pin guide 1400 is illustrated in FIG. 14. The pin        guide 1400 can have a horizontal base 1402 with two parallel and        equal length cannulas 1406, 1408 extending away from the base.        The cannulas 1406, 1408 can be arranged so that they can be used        to contact a patient's bone to allow two pins to be inserted,        one through each cannula, such that a sensor can be attached to        the bone via the pins. For example, the probes 1204, 1206 can be        extended through the cannulas 1406, 1408 to contact the femur.    -   9. Sets of metal pins, as known in the art.

Methods of the Invention

For ease of understanding and gaining a better appreciation of thesubject matter of the present invention as a whole, a representativeexample describing parts of a knee joint replacement procedure ispresented in detail below. It will be expressly understood, however,that the particular preferences and optimal details of this specificexample are neither restrictive nor limiting of the method and system asa whole, and that many variations of the exemplary method and system areenvisioned which may be advantageously and beneficially employed.

The methodology and system of the present invention can reveal angularposition of the patient's lower limb long bones throughout the course ofan operation. These position angles can, in turn, be used as referencepoints to determine the appropriate angular orientation of instrumentsused for surgical preparation of the patient's native bone, andconsequently for placing a prosthesis in the best possible biomechanicalposition.

The methodology for precise intra-operative preparation of a patient'snative bone and placement and positioning of a prosthesis as a surgicalimplant can be performed in accordance with the following steps:

Step 1: Templating

Templating can include determining different axes and alignments byevaluating routine preoperative anteroposterior (AP) and lateral X-rayimages. These can include the following elements:

-   -   a) A mechanical axis of the femur, a position angle of the FS or        FG in relation to the mechanical axis (e.g., in an AP view), and        a distance of the FS or FG from the joint line. FIG. 17        illustrates one example of an FS 1700 coupled to a femur 102,        and shows a mechanical axis of the femur 1702, a position angle        1704 of the FS 1700 relative thereto, and a distance 1706 of the        FS from the joint line.    -   b) A mechanical axis of the femur and a position angle of the FS        or FG in relation to this axis in a lateral view. FIG. 18        illustrates one example of an FG coupled to a femur 102 at        location 1806, and shows the mechanical axis of the femur 1702,        a position angle 1802 of the FS or FG relative thereto, and a        distance 1804 of the FS or FG from the joint line.    -   c) An axis of the tibia and a position angle of the TG in        relation to this axis in an AP view. FIG. 19 illustrates one        example of an axis of the tibia 1902 and a position angle 1904        of a TG (not shown) relative thereto.    -   d) An axis of the tibia and a position angle of the TG in        relation to this axis in a lateral view. FIG. 20 illustrates one        example of the axis of the tibia 1902 and a position angle 2002        of a TG (not shown) relative thereto.    -   e) A rest position alignment (RPA) of the knee, in AP view. FIG.        21 illustrates one example of an RPA, as shown by an alignment        offset angle 2102 of the mechanical axis of the femur 1702 and        the axis of the tibia 1902.    -   f) A rest flexion angle (RFA) of the knee, in lateral view. FIG.        22 illustrates one exampled of an RFA, as shown by an alignment        offset angle 2202 of the mechanical axis of the femur 1702 and        the axis of the tibia 1902.

The templating step can be completed using image-viewing softwareroutinely employed by surgeons. Such software can include ArthroPlan, adigital templating software that includes tools and templates for thispurpose and is available from ArthroCAD, Inc., of Ayer, Mass.

The templating step can be performed at any time and in any place. Insome embodiments, it can be completed before starting an operation. Theremaining steps described below can be done during the procedure in anoperating room, e.g., after induction of anesthesia, as well as afterprepping and draping a patient's lower limb in a fashion known in theart.

Step 2: Placement of the Femur Sensor (FS)

First, the pin guide 1400 can be used to place two pins in a patient'sfemur that can be used to secure the femur sensor (FS) relative thereto.The two cannulas 1406, 1408 of the pin guide 1400 can be passed throughtwo incisions (e.g., 3 mm incisions in some embodiments) made by asurgical knife into the skin over a predetermined location along theshaft of the femur, until a tip of both cannulas 1406, 1408 comes intocontact with the bone. Two attachment pins (not shown) can then bepassed through the cannulas 1406, 1408 and driven into the femoralshaft. The tips of both cannulas 1406, 1408 should remain in contactwith the bone when the pins are being placed in the femur. The pin guide1400 can then be removed. The FS can then be coupled to the pins in amanner known in the art, thereby yielding a device that can look similarto the FG 1200 shown in FIG. 12.

In one embodiment, the predetermined location can be as illustrated inFIG. 17. More particularly, FIGS. 17 and 18 illustrate the possibleplacement of two sensors: the femur sensor (FS) 1700 and the femur guide(FG) 1200 that has a sensor disposed thereon. In FIG. 17 that shows anAP view, the FS 1700 is placed laterally on the femur 102. In FIG. 17,the vertical line shown at 1700 corresponds to the sensor and thehorizontal lines shown at 1700 correspond to the pins on which thesensor is mounted. In this embodiment, the sensor is mounted 150.0 mmsuperiorly to the joint line between the femur and the tibia, as shownby distance 1706. While spacing other than 150.0 mm can be used (such as200.0 mm, for example), the goal is to place the sensor so that itrepresents the straight lateral edge of the femoral shaft. Because thisedge can be estimated as having a 6.37 degree angular difference fromthe mechanical axis of the femur 1702, the orientation of the mechanicalaxis 1702 in the visible plane can be estimated with a high degree ofaccuracy.

The FS 1700 can alternatively be placed in the position 1806 shown inFIG. 18, which provides a side or lateral view. If placed here, thesensor (represented by the vertical line at 1806) is positionedanteriorly to the femur 102. The pins (represented by the horizontallines at 1806) can be placed using the pin guide 1400 in a similarfashion as in the preceding paragraph. In this position, the edge of thebone, and thus the sensor, would extend along an axis having adifference of 1.38 degrees in angulation from the mechanical axis of thefemur 1702 in the illustrated plane, and the orientation of themechanical axis 1702 can be estimated from the sensor data.

Once the pins have been placed in the desired position, the FS 1700 canbe attached to the pins and secured. As is explained in step 6 below,the FG 1200 can be positioned orthogonally to the FS 1700. Accordingly,if the FS 1700 is placed as shown in FIG. 17, the FG can be placed asshown in FIG. 18, and vice versa. The FG 1200 can be used to calibratethe orientation of the FS 1700 such that, after a successfulcalibration, the FG 1200 can be removed and the orientation of themechanical axis of the femur 1702 in both the AP and lateral planes canbe determined using the sensor data from the FS 1700 alone.

Step 3: Placement of the Tibia Sensor (TS)

The pin guide 1400 can be used for placing two attachment pins in theshaft of the tibia at a predetermined location, following the sameprocedure as in Step 2 above. The pins can be placed in a similarfashion to the pins placed in the femur, including using the spacing of150.0 to 200.0 mm inferiorly from the joint line.

Once the pins have been placed in the desired position, the TS can beattached to the pins and secured, thereby yielding a device that can besimilar to the FG 1200 shown in FIG. 12.

Step 4: Establishing Connection and Starting Communication

Both the FS and the TS can be turned on and communication can beestablished with the application software running on the processor unit.This can be confirmed using the application software by changing theposition of the patient's leg and confirming that the changingorientation of the sensors is being tracked by the processor. FIG. 23illustrates one embodiment of a user interface 2300 that can bedisplayed to a user (e.g., via the display 1108). As shown in thefigure, the interface 2300 can show connection status and strength 2302to the various sensors in use, data 2304 related to the position of thefemur, data 2306 related to the position of the tibia, and data 2308related to the alignment and/or position of the knee joint. Further,this data can be toggled between left and right legs of the patientusing switch 2310 in a case where a double knee arthroplasty is beingperformed. Accordingly, a surgeon can confirm connection andcommunication with the various sensors in use by checking the interface(e.g., portion 2302 in particular) and by moving the patient's leg andobserving values shown on the display to confirm that they update.

Step 5: Reproducing the Anatomic Axis of the Tibia

After initial incision and exposure of the tibia, the tibia guide (TG)1300 can be placed in contact with the tibial tubercle and the medialmalleolus bony landmarks of the tibia in a flexion position. Theposition angles of the TG 1300 can be read by the application softwarewhile the leg is held in a stable position. These numbers can be used bythe software to calibrate the orientation readings from the TS as thetrue anatomic and mechanical axes of the tibia. That is, the sensor 1302on the tibia guide 1300 can provide a true orientation of the axis ofthe tibia 1902. This orientation can be compared to the orientation ofthe tibia sensor (TS) and offsets for the measured angles can be stored.These offsets can then be added back to the TS readings to determine theorientation of the axis of the tibia at any time, even as the patient'slower leg is moved and after the TG 1300 has been removed.

Step 6: Reproducing the Anatomic Axis of the Femur

The two pointing probes 1204, 1206 of the FG 1200 can be passed throughthe skin over the anterior side of the femur 102 at a locationdetermined in Step 1 above until both come into contact with the femoralshaft. The FG 1200 can be held against and along the femur in a stableposition for a short while until software reads the position angle. Inthe illustrated embodiment, the FG 1200 can be placed orthogonally tothe FS (e.g., the FG 1200 can be positioned at location 1806 shown inFIG. 18 when the FS 1700 is placed as shown in FIG. 17). The applicationsoftware can then use the FG position angle number and templated anglenumber to calculate the true position angle of the femur in the plane ofthe FG 1200 and the mechanical axis 1702 of the femur 102. This data canbe used to calibrate the FS 1700 for this plane. The FS 1700 can then beused to determine the orientation of the mechanical axis of the femur1702 in both the AP and lateral views shown in FIGS. 17 and 18. Oncesuch a calibration is complete, the FG 1200 can be removed or, in otherembodiments, can be left in place for the remainder of the operation.

In another embodiment, the original position of the pins can be used asthe reference point if determined to be close to an anatomic axis whentemplating.

In another embodiment, the rest flexion angle (RFA) can be used forcalibrating the position angle of the femur readings from the FS 1700.

Step 7: Navigating the Tibial Cut

The electronic sensor unit 1302 can be detached from the TG 1300 andattached to a mechanical external tibial alignment device, such as thedevice 1000 shown in FIG. 10 that is used by surgeons for positioning atibial cutting block. The application software can show the real timeposition angles of the cutting block (because it now has a sensor on itsalignment device 1000) and the calibrated tibial axis informationtransmitted by the TS (which is similar to the FS 1700 and can beattached to the tibia 104 in a similar manner), and can alert thesurgeon to misalignment. The cutting block can be fixed in a desiredposition in a fashion known in the art, and also fixed in a desiredalignment with the tibial axis. A tibial cut can then be made.

Step 8: Navigating the Femoral Cut

The electronic sensor unit 1202 can be detached from the FG 1200 andattached to a mechanical external femoral alignment device, such as thedevice 900 shown in FIG. 9 that is used by surgeons for positioning afemoral distal cutting block. The application software can show the realtime position angles of the cutting block (because it now has a sensorplaced on its alignment device 1000) and the real time position anglesof the mechanical axis of the femur 1702 based on calibrated datatransmitted by the FS 1700. The application software can further alert asurgeon to any misalignment between the cutting block and the mechanicalaxis of the femur 1702. The cutting block can be fixed in a desiredposition in a fashion known in the art, and also fixed in a desiredalignment with respect to the mechanical axis of the femur 1702. Afemoral distal cut can then be made.

The application software can be used to continuously monitor the realtime position angles by receiving data from the electronic positionsensors and calculating the relative angles. The information can bevisually displayed on a computer's screen, or otherwise presented orconveyed to a user. FIG. 23 illustrates one embodiment of an interface2300 that can be displayed to a user and can include position angles andalignment data for the femur, tibia, and knee joint.

Aside from the steps detailed above, known TKA surgical techniques canbe followed during the remainder of the operation. The FS, TS, and pinscan be removed at the end of operation.

Advantages and Benefits of the Invention

The present invention provides a surgeon with many advantages anddesirable benefits over prior art TKA alignment techniques. Among themcan be the following:

Precision: The electronic position sensors can be very precise andsensitive. When the procedure is done properly, the position angles canbe highly accurate. Mechanical devices, on the other hand, can haveaccuracy limitations that result from being positioned visually andwithout a precise calibration.

Ease of Use: The apparatus of the present invention can be set up andused by any member of a surgical team after a short period of training.This is in marked contrast to computerized navigation systems thatrequire a long period of technical training before being used and have alonger learning curve.

Reliability: Taking advantage of precise and accurate components,devices and systems according to the teachings of the present inventioncan provide reliable information to aid in proper alignment.

Simplicity: The present invention employs only a few small basiccomponents and can use any conventional computer processor, PC, orhand-held electronic device. This fact makes the apparatus far lessvulnerable to malfunction and failures; and allows for easierreplacement of component parts if and when necessary. In comparison,computerized navigation requires one or two large camera units and ahighly sophisticated computer, and it uses many different probes forregistration.

Compact Size: The apparatus of the present invention, apart from theaxis guide and the PC in certain embodiments, is very small in size andlight in weight. In practice, the apparatus does not take up anymeaningful space in the operating room and does not need a largeinventory space. In addition, there is no equipment to be maintainedoutside of the operating room.

In comparison, computerized navigation systems can be bulky and heavy.They can only be used in large operating rooms. In addition to theirlarge size, since the system has to be kept out of the sterile operatingfield while the cameras aim at the special spheres with no objectpassing in between them, the true setup requires even more space andlimits the number of the assistants or trainees that can be present.Further, the equipment has to be kept in a storage area when are notbeing used.

Low Cost of Acquisition: The true cost of the present invention isestimated to be low, a small fraction of a computerized navigationsystem.

Time Savings: By helping surgeons to optimally prepare the patient'snative bone during an initial TKA procedure, there is no need toreevaluate and/or recut bones. As a result, the present invention canconsiderably shorten the time needed for completing the operation.

Cost Savings: By shortening the operation time, the present inventionalso lowers the expense of the surgical operation and increases theproductivity of surgeons and operating rooms.

Reduced Morbidity: By properly positioning prosthetic implants at thecorrect anatomical angles, the present invention can increase thedurability of the prosthesis and lower any risk for revision operationsin future. In addition, by shortening the operation time, the risk ofinfection is also lowered.

Increase Patients' Satisfaction: It is obvious that better anatomicalalignment will result in better function and higher patientsatisfaction.

Although the invention has been described by reference to specificembodiments, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but that it have the full scope defined by thelanguage of the following claims.

What is claimed is:
 1. A system for optimizing the alignment of a bonecutting guide for placement of a total knee prosthesis componentcomprising: a first bone sensor having a sensor for determining theorientation of the first bone sensor and a transmitter for transmittingorientation data wirelessly, the first bone sensor being adapted to befixed to a first bone; a first bone guide having a plurality of probesconfigured to contact anatomical features of the first bone to establisha known geometry with respect to a mechanical axis of the first bone,the first bone guide including a first bone guide sensor having a sensordetermining the orientation of the first bone guide and a transmitterfor transmitting orientation data wirelessly; a first bone cutting guidehaving one or more features configured for attactment to the patient'sanatomy proximate to the first bone, the first bone cutting guideincluding a first bone cutting guide sensor having a sensor determiningthe orientation of the first bone cutting guide and a transmitter fortransmitting orientation data wirelessly; a second bone sensor having asensor for determining the orientation of the second bone sensor and atransmitter for transmitting orientation data wirelessly, the secondbone sensor being adapted to be fixed to a second bone; a second boneguide having a plurality of probes configured to contact anatomicalfeatures of the second bone to establish a known geometry with respectto a mechanical axis of the second bone, the second bone guide includinga second bone guide sensor having a sensor determining the orientationof the second bone guide and a transmitter for transmitting orientationdata wirelessly; a second bone cutting guide having one or more featuresconfigured for attachment to the patient's anatomy proximate to thesecond bone, the second bone cutting guide including a second bonecutting guide sensor having a sensor determining the orientation of thesecond bone cutting guide and a transmitter for transmitting orientationdata wirelessly; and a processing unit comprising a computer processorcoupled to a non-transitory memory and a display, the memory storingsoftware instructions causing the computer processor to: i) receiveorientation data wirelessly from the first bone sensor; ii) receiveorientation data wirelessly from the first bone guide sensor; iii) applythe orientation data from the first bone guide sensor and the first bonesensor to calculate angular offsets that calibrate the first bonesensor's orientation data to reflect the orientation of the mechanicalaxis of the first bone; iv) receive orientation data wirelessly from thefirst bone cutting guide sensor; v) display to a user a differencebetween the orientation of the mechanical axis of the first bone and theorientation of the first bone cutting guide: vi) receive orientationdata wirelessly from the second bone sensor; vii) receive orientationdata wirelessly from the second bone guide sensor; viii) apply theorientation data from the second bone guide sensor and the second bonesensor to calculate angular offsets that calibrate the second bonesensor's orientation data to reflect the orientation of the mechanicalaxis of the second bone; ix) receive orientation data wirelessly fromthe second bone cutting guide sensor; and x) display to a user adifference between the orientation of the mechanism axis of the secondbone and the orientation of the second bone cutting guide.
 2. The systemof claim 1, wherein the first bone is a tibia.
 3. The system of claim 2,wherein the first bone guide includes at least one tubercle probe and atleast one malleolus probe.
 4. The system of claim 3, wherein the firstbone guide further includes a spine probe and at least two malleolusprobes.
 5. The system of claim 2, wherein the first bone cutting guideis arranged to guide a cut that is oriented at a 90 degree angle to themechanical axis of the first bone.
 6. The system of claim 1, wherein thefirst bone is a femur.
 7. The system of claim 6, wherein the first boneguide is configured to contact the femoral shaft.
 8. The system of claim7, wherein the first bone guide includes two parallel and equal heightprobes for contacting the femoral shaft.
 9. The system of claim 1,wherein the first bone is a tibia and the second bone is a femur.
 10. Amethod for aligning a cutting guide for total knee arthroplasty on apatient comprising: attaching a first bone sensor to the patient's firstbone, the first bone sensor having a sensor for determining theorientation of the first bone sensor and a transmitter for transmittingorientation data wirelessly; contacting a first bone guide to thepatient's first bone, the first bone guide having a plurality of probesconfigured to contact anatomical features of the first bone to establisha known geometry with respect to a mechanical axis of the first bone,the first bone guide including a first bone guide sensor having a sensordetermining the orientation of the first bone; comparing the orientationdata from the first bone sensor to the orientation data from the firstbone guide sensor to calibrate the first bone sensor with respect to amechanical axis of the first bone; applying a first bone cutting guideto the patient's first bone, the first bone cutting guide having one ormore features for attaching to the patient's anatomy proximate to thefirst bone, the first bone cutting guide including a first bone cuttingguide sensor having a sensor determining the orientation of the firstbone cutting; comparing the orientation data from the first bone sensorwith the orientation data from the first bone cutting guide sensor todetermine the alignment between the first cutting guide and themechanical axis of the patient's first bone; attaching a second bonesensor to the patient's second bone, the second bone sensor having asensor for determining the orientation of the second bone sensor and atransmitter for transmitting orientation data wirelessly; contacting asecond bone guide to the patient's second bone, the second bone guidehaving a plurality of probes configured to contact anatomical featuresof the second bone to establish a known geometry with respect to amechanical axis of the second bone, the second bone guide including asecond bone guide sensor having a sensor determining the orientation ofthe second bone guide; comparing the orientation data from the secondbone sensor to the orientation data from the second bone guide sensor tocalibrate the second bone sensor with respect to a mechanical axis ofthe second bone; applying a second bone cutting guide to the patient'ssecond bone, the second bone cutting guide having one or more featuresfor attaching to the patient's anatomy proximate to the second bone, thesecond bone cutting guide including a second bone cutting guide sensorhaving a sensor determining the orientation of the second bone cuttingguide; and comparing the orientation data from the second bone sensorwith the orientation data from the second bone cutting guide sensor todetermine the alignment between the second bone cutting guide and themechanical axis of the patient's second bone.
 11. The method of claim10, wherein the first bone is a tibia.
 12. The method of claim 11,wherein the first bone cutting guide is arranged to guide a cut that isoriented at a 90 degree angle to the mechanical axis of the first bone.13. The method of claim 10, wherein the first bone is a femur.
 14. Themethod of claim 10, wherein the first bone is a tibia and the secondbone is a femur.